Acetals acetal type

Pos twe-Tone Photoresists. The ester, carbonate, and ketal acidolysis reactions which form the basis of most positive tone CA resists are thought to proceed under specific acid catalysis (62). In this mechanism, illustrated in Figure 22 for the hydrolysis of tert-huty acetate (type A l) (63), the first step involves a rapid equihbrium where the proton is transferred between the photogenerated acid and the acid-labile protecting group ... 

Some of the other eucalyptus oils of commercial importance iaclude the Chinese eucalyptus, a camphor/ciaeole-type oil E. citriodora Hook, a citroaeUal-type oil E. staigeriana F.v. Muel., a citral-type oil and E. macarthuri H. Deane Maiden, a geranyl acetate-type oil. 

The adhesives (qv) used to form tube seams and bag bottoms include unborated dextrin, borated dextrin, casein, latex—casein, latex, poly(vinyl acetate), vinyl acetate copolymers, and hot-melt materials (10,27). Dextrin and casein adhesives are more commonly used in the production of grocery sacks vinyl acetate-type adhesives are commonly used in ah paper multiwah bags. The hot-melt adhesives are typicahy used to tack the phes of the multiwah bag together and to form the seam and bottom joints when polymer film phes or coated paper phes are used in bag constmction. 

Vinyl chloride polymers are produced in two main types, homopolymers and copolymers, usually with vinyl acetate. Both types can be plasticized by a wide variety of plasticizers (qv), usually esters. Rigid or unplasticized PVC is used extensively for pipe. The plasticized material is used largely in floor coverings. The homopolymer itself is inherently fire-resistant, but addition of plasticizers, unless they are especially fire-resistant, considerably reduces this characteristic (see Elame retardants). 

Historically, simple Vz-alkyl ethers formed from a phenol and a halide or sulfate were cleaved under rather drastic conditions (e.g., refluxing HBr). New ether protective groups have been developed that are removed under much milder conditions (e.g., via nucleophilic displacement, hydrogenolysis of benzyl ethers, and mild acid hydrolysis of acetal-type ethers) that seldom affect other functional groups in a molecule. 

Analogous acyl migrations occur with dienol acetates of type (238) and (239), yielding products from the two possible recombinations—(240)/(241) and (243)/(244), respectively—besides the products of reductive acetyl elimination (see Experiment b below). 

The Izod impact test may indicate the need to avoid inside sharp corners on parts made of such materials. For example, nylon and acetal-type plastics, which in molded products are among the toughest materials, are notch-sensitive and register relatively low values on the notched Izod impact test. 

Many environmental toxins interact with specific cellular receptors, including enzymes, ion channels and ion pumps, and thus provide natural tools for the study of cellular signalling pathways. Palytoxin, a compound isolated from the coelen-terate of genus Palythoa, is one such useful and intriguing compound. The structure of palytoxin was first determined in 1981 independently by Hirata (7) and Moore (2). As one of the most potent marine toxins known, palytoxin has been studied in a variety of systems ranging from erythrocytes to neurons. As a tumor promoter of the non 12-O-tetradecanoylphorbol-13-acetate (TPA) type, palytoxin can also be studied in the context of a growth control system. 

Other blockers of epithelial Cl -channels are of the aryl-amino-benzoate type or phenoxy-acetic-acid type [70]. Very few systematic surveys comparing different classes of blockers in one type of Cl -channel are available at this stage. One such study has been performed in membrane vesicles from kidney cortex [80]. In this study IAA-94 and NPPB (cf. Fig. 2) turned out to be the most potent blocker of conductive Cl -flux. In another systematic survey the Cl -conductance of the sweat duct was examined, and it was found that dichloro-DPC (Fig. 2) was the most potent inhibitor of the transepithelial Cl -conductance [90]. 

Smaller aldehydes form cyclic acetal-type oligomers readily in aqueous conditions.60 Diols and polyols also form cyclic acetals with various aldehydes readily in water, which has been applied in the extraction of polyhydroxy compounds from dilute aqueous solutions.61 E in water was found to be an efficient catalyst for chemoselective protection of aliphatic and aromatic aldehydes with HSCH2CH2OH to give 1,3-oxathiolane acetals under mild conditions (Eq. 5.7).62... 

Examples of the oxidative cleavage/bis-hetero-Diels-Alder domino sequence of compounds of type 7-124 to give acetals of type 7-125 are listed in Scheme 7.34. This shows that the reaction is high-yielding and can be carried out under rather mild conditions. 

Scheme 11.10. INAS reaction of homoallyl acetates of type 34. For details, see Table 11.6.

In sludge anionic and non-ionic surfactants carboxylic acids hhydroxybutyrate hydroxy valerate chloroaliphatic compounds chlorophenols polychlorobiphenyls 4-nitrophenol mixtures of organic compounds chlorinated insecticides, phenoxy acetic acid type herbicides and organotin compounds. 

Category I Substituent Assemblies The first rationalization of the observation that in acetal-type compounds the a-SCS of the second oxygen function is considerably smaller than that of the first (70,239) was the assumption that an adjacent oxygen atom reduces the polarizability of the a-carbon atom, so that it cannot be polarized as effectively by the second substituent (142). 

Other acetal-type protecting groups (tetrahydrofurfuryl ethers, methoxymethyl ethers, 1,3-dioxolanes) are also considered to be incompatible with oxidising agents. 

Suganuma, M., et al., Okadaic acid an additional non-phorbol-12-tetradecanoate-13-acetate-type tumor promoter, Proc. Natl. Acad. Sci. U.S.A., 85, 6, 1768, 1988. 

Thus, an estimation can be made of the hydrophilicity of the crown ring. The acetal-type crown ring obtained from hexaethyl-ene glycol and a higher aliphatic aldehyde is estimated to be e-quivalent to about four OE units in an alkyl POE monoether, from our study of the cloud point (11). Moroi et al. concluded, from a comparison of the cmc, that a diaza-18-crown-6 is equivalent to 20 OE units in the usual type of nonionic (12). Okahara s group evaluated the effective HLB based on the cloud point, phenol index and phase-inversion-temperature in emulsion of oil/water system and they concluded that 18-crown-6 and monoaza-18-crown-6 rings with dodecyl group are approximately equivalent to 4.0 and 4.5 units, respectively, of OE chains with the same alkyl chain (17). 

Initially all membranes were exposed to 3 ppm chlorine in buffer solutions at pH levels of 3.0, 5.8, and 8.6 for three weeks. Both cellulose acetate type membranes C-2 and V-1 were unaffected by chlorine under these conditions. Continued exposure at higher chlorine levels did not alter baseline membrane performance. For example, membrane C-2 exposed to 125 ppm chlorine for 10 days at pH 3 continued to perform at baseline levels. In subsequent work, cellulose acetate membranes were also found to be unresponsive to bromine, iodine, and chlorine dioxide. It can be generally concluded that cellulose acetate type membranes are halogen resistant. 

A facile acid-catalyzed double cyclization of A,A-dibenzylaminoacetaldehyde dialkyl acetals of type 125 has been known to generate l-azadibenzo[c,/]bicy-clo[3.3.1]nona[3,6]dienes 126 in high yields 120,121,147). A novel and convenient synthesis of ( )-amurensinine (25) and ( )-reframine (28) (Scheme 25) proceeds from the quaternary salt 127, where proper choice of base and reaction... 

C-Glycosyl compounds are important molecular targets as they occur in Nature and have interesting biological properties (for reviews on C-glycosylation, see [72-75]). Chain extensions of aldonolactones have been employed to create C-C bond formation at the anomeric center. Claisen-type reactions of aldono-1,4-lactones (e.g., 9, 55) with acetone or acetophenone (Scheme 17) generate hemi-acetals of type 56a-c [76]. Similarly, lactone 55b reacts with CHsCN/NaH to give hemiacetal 57. 

N-Acylation of 2-methyl-5,6-dihydro-4/f-l,3-thiazine with cinnamoyl chloride in the presence of triethylamine furnishes ( )-l-(2-methylenetetrahydro-l,3-thiazin-3-yl)-3-arylprop-2-en-l-ones 122. These products undergo hydrolysis readily due to the j jA -ketene acetal-type bonds present in the molecules and are therefore not stable. Thus ( )-3-(3-(4-methoxyphenyl)acrylamido)propyl ethanethioate 123 is isolated in 92% yield from the corresponding thiazine after column chromatography on Si02 or AI2O3 <2001S135>. 

Acidic compounds of type R—XH, which are able to protonate thiocarbonyl ylides, also undergo 1,3-addition leading to products of S,S-, S,0-, or 5,A-acetal type (Scheme 5.20). Thiophenols and thiols add smoothly to thiocarbonyl ylides generated from 2,5-dihydro-l,3,4-thiadiazoles (36,38,86,98,99). Thiocamphor, which exists in solution in equilibrium with its enethiol form, undergoes a similar reaction with adamantanethione (5)-methylide (52) to give dithioacetal 53 (40) (Scheme 5.21). Formation of analogous products was observed with some thiocarbonyl functionalized NH-heterocycles (100). 

The oxonium ion intermediate of the type 34 normally collapses by the attack of a nucleophile OH or OAc to yield a masked aldehyde or hemi-acetal-acetate group. However, in this particular case the approach of... 

T. Mukaiyama, M. Ohshima, and M. Murakami, 2-Benzyloxy-propene A novel protective reagent of hydroxyl groups, Chem Lett 265 (1984) T. Mukaiyama, M. Ohshima, H. Nagaoka, and M. Murakami, A novel acid-resistant acetal-type protective group for alcohols, Chem. Lett 615 (1984). 

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